The trend of ever increasing magnetic storage density and data transfer rates requires magnetic materials with superior characteristics. Soft magnetic materials with high magnetic flux density Bs are of great interest for thin film write head applications. At high operating frequencies, eddy currents in the write head cause a reduction in the permeability of the pole material, which in turn reduces the efficiency of the head.
Lamination of the magnetic pole material with insulation layer is commonly used as a means to suppress the eddy-current loss during the high frequency operation as disclosed in U.S. Pat. No. 5,750,275, by Katz et al., entitled THIN FILM HEADS WITH INSULATED LAMINATION FOR IMPROVED HIGH FREQUENCY PERFORMANCE, issued May 12, 1998, herein incorporated by reference in its entirety. Laminating with an insulative material, however, also reduces the Bs of the structure.
Recently high Bs Co-based or Fe-based amorphous alloys with high intrinsic electrical resistivity xcfx81 have also received great attention, such as disclosed in U.S. Pat. No. 5,725,685, by Hayakawa et al., entitled SOFT MAGNETIC ALLOY THIN FILM WITH NITROGEN-BASED AMORPHOUS PHASE, issued Mar. 10, 1998. Such alloys, however have relatively low Bs, typically less than about 15 kG, and often suffer from poor thermal stability and corrosion resistance.
Other work has shown increasing resistivity of FeXN sputtered films using N2, but, this work has also shown a corresponding reduction in coercivity. Such work has shown FeXN formed primarily of xcex1 phase or body centered cubic Fe, with only a small portion of xcex3 phase or face centered cubic Fe4N.
What is desired is a soft magnetic material having high magnetic moment Bs, low magnetostriction xcexs, high permeability, high frequency performance, corrosion resistance, and thermal stability.
A preferred method of the present invention provides an improved thin film for carrying magnetic flux. With the preferred method, the magnetic thin film may be formed by depositing Fe by reactive sputtering using N2 to form a thin film comprising xcex1-Fe and xcex3-Fe4N. With this method, the relative percentage of xcex3-Fe4N in the deposited film is increased to provide expanded lattice constants for both the xcex1-Fe and the xcex3-Fe4N. Increasing xcex3-Fe4N increases resistivity while expanded lattice constants provide improved coercivity in higher resistivity films.
Increasing the percentage of xcex3-Fe4N to provide expanded lattice constants for both the xcex1-Fe and xcex3-Fe4N may be accomplished by adjusting sputtering power, N2 gas percentage, a flow rate of N2, and substrate bias. In some embodiments, high sputtering power of about 3-4 kW with about 15-30 percent of N2 may be used to sputter FeX, where X is selected from the group consisting of Rh, Ta, Hf, Al, Zr, Ti, Ru, Si, Cr, V, Sr, Nb, Mo, Ru, and Pd, to provide expanded xcex1-Fe and the xcex3-Fe4N lattice constants.
In preferred methods and embodiments of the present invention, high resistivity low coercivity FeXN thin films are possible. In some embodiments, FeXN films having resistivity values greater than about 50 xcexcxcexa9cm, 80 xcexcxcexa9cm, 100 xcexcxcexa9cm, 115 xcexcxcexa9cm, or more, for coercivity values less than about 10 Oe, 5 Oe, or 3 Oe are possible. Furthermore, these results may be obtained for values of Bs greater than around 12 kG to 17 kG.
Embodiments of the improved thin film of the present invention may be used for pole or shield structures in magnetic heads, such as disk, tape, or other type data storage and retrieval apparatuses, to improve high frequency performance.